This invention relates to improvements in framing structures for buildings and relates particularly to an improved portal frame structure--also knwon as "open" or "clear span" structures--for the construction of buildings or shelters.
Portal frames in buildings such as light industrial factories, warehouses, agricultural buildings and the like are presently fabricated from metal sections of both hot-rolled and cold-formed manufacture.
Hot rolled members, which are generally `I` beams of various dimensions, are commonly used as framing members in portal buildings but their use requires substantial engineering design and fabrication detailing which results in a relatively expensive building construction. Further, because much of the fabrication is usually carried out in a welding shop and the components subsequently transported to the site for erection, difficulties are encountered in transporting the fabricated components.
Cold-formed sections have been used for the construction of relatively small buildings, such as domestic workshops, garages, farm sheds and the like, when the relatively thin walled sections are used well within their theoretical design capacity. Cold-formed sections used as primary members of a building frame are usually of lipped channel section or `C` section which is asymmetrical and therefore loading on such members introduces significant secondary stressing which limits the member's structural capacity.
Further, in portal building frames, stresses are a maximum at the connections between the members, particularly the knee and ridge connections. Typical knee connections involve the use of end plates and cleats welded to the various members and subsequently bolted together. This connection system is similar to that used in connecting hot-rolled members.
Another connection system is disclosed in Australian Patent Application No. 25493/77 of Fletcher Industries Limited which discloses the use of a connector to and between adjacent portal members where the connector is attached, as by bolts, to the webs of the C-shaped portal members.
However, such connectors are located at the points of greatest stress in the frame and the bolted web connections introduce relatively large additional secondary stresses into the C-shaped portal members.
It is therefore desirable to provide a portal building framing system which uses single cold-formed metal sections as the framing structure and has connectors between the sections which increases the capacity and span of the sections heretofor acceptable.
It is also desirable to provide a portal building frame which is relatively simple to fabricate and transport to site for erection.
It is also desirable to provide a protal building framing system which enables secondary members, such as purlins and girts, to be secured to the primary portal members so as to give rise to a minimum of secondary stresses in the portal members.
It is also a desirable feature to provide a portal building framing system which uses standard sized portal members for a variety of sizes of buildings without the need to individually detail the design and fabrication of the portal members and connections.